Anesthetic dispensing devices with an evaporation chamber are frequently used in conjunction with anesthesia apparatuses in order to enrich a carrier gas with a volatile anesthetic. In the liquid state, the anesthetic is filled into the evaporation chamber, which is usually equipped with a wick device, which becomes saturated with the anesthetic and on its surface finally discharges the evaporating anesthetic liquid to the carrier gas flowing through the evaporation chamber. The concentration of the anesthetic in the anesthetic gas fed to the patient must be adapted as a function of the kind of anesthesia as well as the progress of the operation. A hand wheel, by means of which the dispensing unit can be adjusted in a specific manner in the anesthetic evaporator, is provided for this purpose in prior-art anesthetic evaporators.
An anesthetic dispensing device of this type with evaporation chamber, in which the portion of the gaseous anesthetic in the anesthetic gas can be adjusted in a specific manner, is known from DE 25 07 261 A1. The principal portion of the carrier gas stream at first flows in a bypass line past the evaporation chamber. By contrast, a small portion of the carrier gas is fed by a branching of the carrier gas stream into the evaporation chamber, in which it is enriched with the anesthetic until it is saturated and finally flows out of the evaporation chamber via an adjustable dispensing gap. The part of the carrier gas stream thus enriched with anesthetic is in turn added to the part of the carrier gas stream, which leaves the bypass channel unchanged, in order to thus generate the anesthetic gas stream needed for the anesthesia of the patient. The concentration of the anesthetic in the anesthetic gas stream can be adjusted in this connection by means of a variation of the dispensing gap in the dispensing unit, with the portion of the anesthetic in the anesthetic gas being changed by means of changing the dispensing gap width in a specific manner. Via the anesthetic gas outlet, this gas is first fed to an anesthesia apparatus and finally fed to the patient to be treated.
The dispensing gap described is designed as a ring gap which is formed by a flat surface of a hollow ring body and the flat surface of a hollow cylinder arranged in the hollow ring body. Temperature-related changes in the dispensing gap can be caused by temperature fluctuations in the surrounding area of the anesthetic dispensing device as well as because of the cooling off of the evaporation chamber, which brings about a lowering of the saturation concentration of the anesthetic vapor. To also compensate temperature-related changes in the dispensing gap, a temperature compensation is provided in the anesthetic dispensing device described in DE 25 07 261 A1. For this purpose, the hollow cylinder and the hollow ring body are made of different materials, with the hollow cylinder having a smaller coefficient of thermal expansion than the hollow ring body. In case of temperature changes in the evaporation chamber, the different coefficients of thermal expansion bring about a path of the flat surface, with which the height of the ring gap is changed. The height of the ring gap and thus the free cross section can be changed by providing suitable adjusting screws for adjusting via the ring body.
Furthermore, an anesthetic dispensing device, which has an especially low-friction adjustment of a dispensing cone with respect to a cone sleeve, is known from DE 10 2005 032 154 B3. In this case, the dispensing cone is fastened in a manner capable of performing strokes with respect to the cone sleeve by means of two membrane elements spaced apart in parallel. A movement of the dispensing piston is carried out mechanically either by means of a hand wheel or by means of an electric direct drive.
It is problematic in the solutions known from the state of the art that, on the one hand, that a temperature compensation is accomplished with comparatively complicated measures. In particular, the selection of suitable materials as well as the manufacture and the adjustment of correspondingly accurately adjustable dispensing elements require a considerable technical effort and are economically costly. In order to guarantee a corresponding temperature compensation, it is known to adjust an air stream that flows around the dispensing unit by means of mechanically acting mechanisms in a suitable manner.